TM 5-813-8
Assume that:
=
The water contains 1,000 parts per million as CaCO3, 2,650 parts per million SO4 as total sulfate and is at pOH =
11. Assume that the temperature is close to 64 degrees Fahrenheit and that there is no ion pairing of SO4 other
The pKsp of calcium sulfate is given as 3.6.
The pKa of sulfuric acid second dissociation is given as 1.92.
The density of the saline water sample is 1,025 grams/liter at 64 degrees Fahrenheit.
To convert calcium and sulfate concentrations in the expected brine (density = 1025 grams/liter) to molarity use the
following calculations:
∴ Unless other ions complex Ca++ or SO4, scaling will be a problem at 64 degrees Fahrenheit. (See figure 5-2.)
A-4. Ion- exchange desalination. Apermanent installation is proposed near Haftrak,
Arizona. The potable weater treatment system will serve a resident population of 2,000. Use TM 5-813-1 to obtain water
consumption per day. The calculation is as follows:
150 gallons
2,000 persons x day Person x 1.5 capacity factor = 450,000 gallons per day
The area is hot and dry, with annual average maximum daily air temperature of 55 degrees Fahrenheit and a net pan
evaporation of approximately 87 inches. Ground water is available, as well as an average chemical analysis.
A-17
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